1. Field of the Invention
The present invention relates to a wet-type friction clutch plate achieving frictional engagement between frictional slide faces to transmit torque between rotary members.
2. Description of the Related Art
An example of a wet-type friction clutch plate is in a power transmission device disclosed in Japanese Patent Laid Open Publication No. 11-208303.
The power transmission device is installed on, for example, a propeller shaft of a 4WD (four-wheel drive) vehicle. Between an outer rotary member on the propeller shaft and an inner rotary member on a drive pinion shaft, wet-type friction clutch plates are arranged to engage in a rotation direction. When the clutch plates receive axial thrust and the propeller shaft and drive pinion shaft rotate relative to each other, the clutch plates frictionally engage with each other to transmit torque between the shafts.
A space between the outer and inner rotary members is sealed to contain lubricant and accommodate the clutch plates. The lubricant maintains lubrication between the clutch plates.
An example of a wet-type friction clutch plate applicable to the power transmission device is disclosed in Japanese Patent Laid Open Publication No. 01-145438. This clutch plate has a grid of grooves on a frictional slide face to secure engagement and prevent detrimental slippage. The grooves keep lubricant within them while maintaining the drainage thereof.
Simply forming such a grid of grooves on a frictional slide face of a wet-type friction clutch plate, however, reduces friction only to some extent, destabilizes torque transmission, and sometimes produces excessive torque. To cope with such excessive torque, reinforced parts must be employed in the power transmission device, thereby increasing the size and weight of the device. In addition, the grooves cause shuddering noise when clutch plates slide on each other.
The wet-type friction clutch plate has a xcexc-v characteristic, wherein xcexc is a coefficient of friction on a frictional slide face of the clutch plate and v is a relative rotational speed of the clutch plate relative to an opposite clutch plate that slides on the clutch plate in question. When xcexc increases with an increase in v, it is a positive xcexc-v inclination, and when xcexc decreases with an increase in v, it is a negative xcexc-v inclination. The negative xcexc-v inclination causes self-excited vibration, destabilizes torque transmission, and produces shuddering noise.
In this way, simply forming a grid of grooves on a frictional slide face of a wet-type friction clutch plate causes various problems.
An object of the present invention is to provide a wet-type friction clutch plate capable of stably transmitting torque and preventing shuddering noise.
A first aspect of the present invention provides a wet-type friction clutch plate having a grid of grooves formed on a frictional slide face that frictionally engages with an opposite clutch plate. At least one of the sectional shape and plan shape of each of the grooves is configured to provide the frictional slide face with a xcexc-v characteristic that xcexc increases with an increase in v to prevent self-excited vibration during frictional engagement of the wet-type friction clutch plate with the opposite clutch plate, wherein xcexc is a coefficient of friction on the frictional slide face and v is a relative rotational speed of the wet-type friction clutch plate relative to the opposite clutch plate.
A second aspect of the present invention provides each of the grooves of the first aspect with a wedge-shaped cross section.
A third aspect of the present invention provides each of the grooves of the second aspect with a V-shaped cross section having symmetrically inclined side walls.
A fourth aspect of the present invention provides each of the grooves of any one of the first to third aspects with a cross section having a curve between each groove side wall and the frictional slide face.
A fifth aspect of the present invention provides each intersection of the grooves of any one of the first to third aspects with a cross section having a curve between each side wall of the intersection and the frictional slide face.
A sixth aspect of the present invention provides each intersection of the grooves of any one of the first to third aspects with rounded corners in a plan view to widen the area of the intersection.
A seventh aspect of the present invention sets the depth of the grooves of any one of the first to third aspects in a range of 0.004 mm to 0.03 mm.
An eighth aspect of the present invention forms the grooves of any one of the first to third aspects by pressing the frictional slide face with the depth of the grooves set in a range of 0.004 mm to 0.03 mm in a radially intermediate area on the frictional slide face.
A ninth aspect of the present invention provides an electromagnetic friction clutch employing the wet-type friction clutch plate of any one of the first to eighth aspects. The electromagnetic friction clutch includes inner and outer rotary members coaxially arranged to rotate relative to each other, a main clutch interposed between the inner and outer rotary members to increase and decrease frictional engagement in response to axial thrust and transmit torque between the inner and outer rotary members through the frictional engagement when the inner and outer rotary members rotate relative to each other, a pilot clutch to achieve frictional engagement in response to electrically controlled electromagnetic force, and a converter acting on the frictional engagement of the pilot clutch, to convert the frictional engagement into thrust to the main clutch. At least one of the main clutch and pilot clutch employs the wet-type friction clutch plate of any one of the first to eighth aspects.
The first aspect forms a grid of grooves on a frictional slide face of a wet-type friction clutch plate that frictionally engages with an opposite clutch plate. At least one of the sectional shape and plan shape of each of the grooves is configured to provide the frictional slide face with a xcexc-v characteristic that xcexc increases with an increase in v to prevent self-excited vibration during frictional engagement of the wet-type friction clutch plate with the opposite clutch plate, wherein xcexc, is a coefficient of friction on the frictional slide face and v is a relative rotational speed of the wet-type friction clutch plate relative to the opposite clutch plate. The first aspect stabilizes torque transmission between the wet-type friction clutch plate and the opposite clutch plate and prevents shuddering noise.
In addition to the effects of the first aspect, the second aspect provides each of the grooves with a wedge-shaped cross section. Lubricant in the grooves produces fluid pressure due to a wedge action to smoothly move onto the frictional slide face and increase a lubricant film thickness between the wet-type friction clutch plate and the opposite clutch plate. The second aspect reduces a time lag in a clutch residual torque diminishing period.
The grooves include those oriented in a rotation direction of the clutch plate and those oriented in a direction orthogonal to the rotation direction. If the grooves orthogonal to the rotation direction have sharp edges, they will damage the opposite clutch plate. Providing the grooves with wedge-shaped cross sections is helpful to form an obtuse angle between a side wall of each groove and the frictional slide face, thereby eliminating sharp edges from the grooves and preventing the damage of the opposite clutch plate.
In addition to the effects of the second aspect, the third aspect provides each of the grooves with a V-shaped cross section having symmetrically inclined side walls. The third aspect realizes the effects of the second aspect on each side wall of the grooves.
In addition to the effects of the first to third aspects, the fourth aspect provides each of the grooves with a cross section having a curve between each groove side wall and the frictional slide face. The fourth aspect prevents the damage of the opposite clutch plate, smoothly passes lubricant, maintains a uniform lubricant film thickness, and suppresses a stick-slip phenomenon.
The curves at the grooves prevent the damage of groove edges during a surface hardening process that employs, for example, a polishing process such as shot peening or shot blasting or barrel polishing to remove an oxide film from the frictional slide face.
In addition to the effects of the first to third aspects, the fifth aspect provides each intersection of the grooves with a cross section having a curve between each side wall of the intersection and the frictional slide face. The fifth aspect prevents the damage of the opposite clutch plate, smoothly passes lubricant, maintains a uniform lubricant film thickness, and suppresses a stick-slip phenomenon.
The curves at the groove intersections prevent the damage of intersection edges during a surface hardening process to remove an oxide film.
In addition to the effects of the first to third aspects, the sixth aspect provides each intersection of the grooves with rounded corners in a plan view to widen the area of the intersection and sufficiently maintain lubricant at the intersection.
In addition to the effects of the first to third aspects, the seventh aspect sets the depth of the grooves in a range of 0.004 mm to 0.03 mm, to sufficiently maintain lubrication on the frictional slide face.
The seventh aspect secures fine pitches and fine frictional slide areas among the grooves, to smoothly transmit torque through frictional engagement and prevent shuddering noise.
In an electromagnetic friction clutch employing the wet-type friction clutch plates each of the seventh aspect driven by electrically controlled electromagnetic force, the grooves shallower than 0.03 mm secure magnetic lines of force to provide a required electromagnetic force. If the grooves are too deep, they increase a clutch-to-clutch space, to block magnetic lines of force. The grooves shallower than 0.03 mm stabilize magnetic attraction and realize sufficient frictional engagement.
The grooves having wedge- or V-shaped cross sections of fixed opening angles reduce frictional slide areas as the depth of the grooves increases. The grooves shallower than 0.03 mm maintain proper frictional slide areas to secure proper frictional engagement.
In addition to the effects of the first to third aspects, the eighth aspect forms the grooves by pressing the frictional slide face with the depth of the grooves set in a range of 0.004 mm to 0.03 mm in a radially intermediate area on the frictional slide face. At the location where the grooves tend to become shallower during pressing, the eighth aspect secures the depth of the grooves within the range of 0.004 mm to 0.03 mm, so that all grooves on the frictional slide face may secure the depth of 0.004 mm to 0.03 mm. The eighth aspect easily controls the depth of the grooves.
In addition to the effects of the first to eighth aspects, the ninth aspect provides an electromagnetic friction clutch employing the wet-type friction clutch plate of any one of the first to eighth aspects. The electromagnetic friction clutch includes inner and outer rotary members coaxially arranged to rotate relative to each other, a main clutch interposed between the inner and outer rotary members to increase and decrease frictional engagement in response to axial thrust and transmit torque between the inner and outer rotary members through the frictional engagement when the inner and outer rotary members rotate relative to each other, a pilot clutch to achieve frictional engagement in response to electrically controlled electromagnetic force, and a converter acting on the frictional engagement of the pilot clutch, to convert the frictional engagement into thrust to the main clutch. At least one of the main clutch and pilot clutch employs the wet-type friction clutch plate of any one of the first to eighth aspects.
When the pilot clutch employs the wet-type friction clutch plate, it shows a good transient characteristic of torque transmission with respect to current ON/OFF operations and minimizes magnetic flux variations under a predetermined current value. The grooves on the clutch plate block magnetic lines of force at a current OFF operation.
When the main clutch employs the wet-type friction clutch plate, it improves the response of the main clutch with respect to a change in transmitted torque or a change in a torque transmission direction. Namely, the wet-type friction clutch plate improves the torque transmission response of the main clutch with respect to the engagement of the pilot clutch that is changed by controlling a current. It also improves the torque transmission OFF response of the main clutch when a control current to the pilot clutch is cut. These effects prevent shuddering noise in the main clutch.